The objectives of this proposal are the synthesis of specific 5,10-seco steroids and their evaluation as selective inhibitors of steroid-transforming enzymes, Some of these steroid analogs are designed as active site-directed irreversible inhibitors of delta 5-3-ketosteroid isomerase, and others are designed as inhibitors of 3 beta-and (3 and 17) beta-hydroxysteroid dehydrogenases and of processes involved in the oxidative degradation of lanosterol and of cholesterol. Others are intended to be reversible inhibitors of these enzymes. The mechanisms by which enzyme inhibition occurs will be studied.